1.What mass of oxygen gas, O2, from the air is consumed in the combustion of 702g of octane, C8H18, one of the principal components of gasoline? 2C8H18 + 25O2 -> 16CO2 + 18H2O.

Approximately .

Explanation:

Look up the following relative atomic mass values on a modern periodic table:

Calculate the molar mass of octane, :

.

Similarly, calculate the molar mass of :

.

How many moles of molecules in of octane, ?

.

Make sure that the chemical equation here is balanced.

In this equation,

Ratio between the two coefficients:

.

Therefore:

.

Rearrange to obtain:

.

It is already determined that . Hence, the number of moles of oxygen gas required will be:

.

What would be the mass of that of ?

.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%

elements make up everything, and they combine to make compounds.

the answer is c